Center pipe for plasma torch, electrode, and plasma torch

ABSTRACT

A center pipe is used in a plasma torch including a base portion and an electrode to supply cooling water into the electrode. The center pipe includes a pipe body and a contact piece. The pipe body has a tube-like shape with a cooling water channel therein. The pipe body is electrically conductive and configured to be electrically connected to an external power source via the base portion. The contact piece is arranged radially outside the pipe body at an intermediate position between a base end surface and a tip end surface of the pipe body. The contact piece is electrically conductive and energizes the electrode through contact with an internal circumferential surface of the electrode. The base end surface is disposed outside the electrode when the center pipe is inserted into the electrode. The pipe body is configured to be electrically connected to the electrode via the contact piece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of a U.S. patent application Ser. No. 15/325,313, which is a U.S. National stage application of International Application No. PCT/JP2015/084161, filed on Dec. 4, 2015, and claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2015-017463, filed in Japan on Jan. 30, 201. The entire contents of U.S. patent application Ser. No. 15/325,313, International Application No. PCT/JP2015/084161, and Japanese Patent Application No. 2015-017463 are hereby incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to a center pipe for a plasma torch, an electrode for the plasma torch, and a plasma torch including the center pipe and the electrode.

Background Information

A plasma torch includes an electrode that acts as the originating point of an arc, and a nozzle disposed so as to cover the electrode. The electrode is attached to an electrode seat of a torch body. The nozzle is attached to the electrode via an insulation guide. The insulation guide positions the nozzle so that the nozzle is disposed concentrically with the electrode. The plasma torch causes a plasma arc to be generated between the electrode and a workpiece through an orifice of the nozzle.

Because the electrode is a consumable, the electrode is attached to the electrode seat of the torch body in a detachable manner. For example, the electrode as described in Japanese Laid-open Patent 2001-47247 has a tip end side cylindrical portion, a flange portion, and a base end side cylindrical portion. The flange portion has an outer diameter greater than that of the tip end side cylindrical portion and the base end side cylindrical portion. The electrode is attached to the electrode seat due to the base end side cylindrical portion being coupled to the inner surface of the electrode seat with a frictional resistance force. Alternatively, a female thread portion is formed on the electrode seat and a male thread portion is formed on the base end side cylindrical portion. The male thread portion of the base end side cylindrical part is screwed onto the female thread portion of the electrode seat, whereby the electrode is attached to the electrode seat.

While the electrode is attached to the electrode seat, the end surface in the axial direction of the flange portion is in contact with the tip end portion of the electrode seat. Moreover, the external circumferential surface of the base end side cylindrical portion is in contact with the internal circumferential surface of the electrode seat. That is, the external circumferential surface of the base end side cylindrical portion and the end surface in the axial direction of the flange portion of the electrode act as energization surfaces with the electrode seat. The electrode and the torch body are electrically connected through the above energization surfaces.

SUMMARY

There is a problem in that the structure of the electrode or of the electrode seat is complex in order for the base end side cylindrical portion and the internal circumferential surface of the electrode seat to be connected in the abovementioned plasma torch. Moreover, when the base end side cylindrical portion and the electrode seat are connected through a threaded structure, a specialized tool is necessary for attaching and detaching the electrode. Furthermore, there is a problem that the torch body of the plasma torch needs to be replaced if the energization surfaces of the base end side cylindrical portion and the electrode seat are damaged due to energization fault.

An object of the present invention is to provide a center pipe for a plasma torch, a contact piece, an electrode, and a plasma torch for which the electrode can be attached and detached easily without a specialized tool, the structure of the electrode or the electrode seat is simplified, and moreover, the replacement of the torch body is unnecessary even when energization fault occurs.

A center pipe according to a first aspect of the present invention is used in a plasma torch for plasma cutting that includes a base portion and an electrode. The center pipe is inserted into the electrode in order to supply cooling water into the electrode. The center pipe includes a pipe body and a contact piece. The pipe body has a tube-like shape including a base end surface and a tip end surface opposite the base end surface in an axial direction of the tube-like shape. The pipe body is configured to be electrically connected to an electrical power source outside of the plasma torch via the base portion. The pipe body includes a cooling water channel therein, and the pipe body is made of an electrically conductive material. The contact piece is arranged radially outside an external circumferential surface of the pipe body at an intermediate position between the base end surface and the tip end surface. The contact piece energizes the electrode through contact with an internal circumferential surface of the electrode. The contact piece is made of an electrically conductive material. The base end surface is disposed outside the electrode when the center pipe is inserted into the electrode. The pipe body is configured to be electrically connected to the electrode via the contact piece.

The cooling water channel of the pipe body may include a first channel extending from the base end surface toward the tip end surface, and the first channel may be tapered such than an internal diameter of the first channel is wider near the base end surface and narrower toward the tip end surface.

The cooling water channel of the pipe body may include a first channel, a second channel, and a third channel. The first channel may extend in the axial direction of the tube-like shape from the base end surface toward the tip end surface. The second channel may extend in the axial direction from a tip end surface side of the first channel toward the tip end surface. The third channel may extend in the axial direction from a tip end surface side of the second channel toward the tip end surface, the third channel reaching the tip end surface. An internal diameter of the third channel may be larger than an internal diameter of the second channel. The third channel may be configured to receive a protruding portion provided on an internal surface of a tip end of the electrode.

The external circumferential surface of the pipe body may include a first external circumferential surface, a second external circumferential surface, and a third external circumferential surface that are disposed axially adjacent one another along the axial direction with the second external circumferential surface being disposed between the first external circumferential surface and the third external circumferential surface. The first external circumferential surface may have a larger external diameter than the second external circumferential surface. The second external circumferential surface may have a larger external diameter than the third external circumferential surface. The first external circumferential surface may surround the first channel.

The pipe body may include a flange portion having a larger external diameter than the first external circumferential surface of the pipe body, the flange portion being disposed at a base end of the pipe body and including the base end surface. The center pipe may be configured such that the electrical connection of the pipe body to the electrical power source outside of the plasma torch is established by contact of the base end surface of the pipe body against the base portion of the plasma torch. The contact piece may be attached to the external circumferential surface of the pipe body.

An electrode according to a second aspect of the invention is for use in a plasma torch for plasma cutting that includes a center pipe having a cooling water channel therein. The electrode includes an electrode body portion and an internal channel. The electrode body portion includes a tip end and a base end. The tip end and the base end are spaced from each other in an axial direction of the electrode. The electrode body portion has a shorter length in the axial direction than the center pipe. The internal channel is configured to receive the center pipe. The internal channel is formed inside the electrode body portion and extends in the axial direction from the base end toward the tip end. A base end surface of the base end of the electrode includes an inlet of the internal channel.

The electrode may include a protruding portion provided on an internal surface of the electrode body portion at the tip end. The protruding portion may protrude toward the base end of the electrode body portion. The protruding portion may be configured and arranged to be at least partially disposed inside a cooling water channel of the center pipe when the electrode and the center pipe are installed in the plasma torch. The protruding portion may fit inside the cooling water channel at a tip end of the center pipe.

A heat resistant insert may be embedded into a tip end surface at the tip end of the electrode. The heat resistant insert may be disposed at least partially inside the protrusion.

At least a portion of an internal circumferential surface of the internal channel may form a first energization surface configured to be in contact with a contact piece of the center pipe. The contact piece may be provided on the center pipe.

A plasma torch according to a third aspect of the invention includes a base portion, a center pipe, and an electrode. The center pipe is inserted into the electrode in order to supply cooling water into the electrode.

The center pipe includes a pipe body and a contact piece. The pipe body has a tube-like shape including a base end surface and a tip end surface opposite the base end surface in an axial direction of the tube-like shape. The pipe body is configured to be electrically connected to an electrical power source outside of the plasma torch via the base portion. The pipe body includes a cooling water channel therein, and the pipe body is made of an electrically conductive material. The contact piece is arranged radially outside an external circumferential surface of the pipe body at an intermediate position between the base end surface and the tip end surface. The contact piece energizes the electrode through contact with an internal circumferential surface of the electrode. The contact piece is made of an electrically conductive material. The base end surface is disposed outside the electrode when the center pipe is inserted into the electrode. A portion of the pipe body extends from the base end surface toward the contact piece. The pipe body is configured to be electrically connected to the electrode via the contact piece. The electrode includes an internal channel having the internal circumferential surface into which the center pipe is inserted. At least a portion of the internal circumferential surface of the internal channel forms a first energization surface, which is in contact with the contact piece.

Effects of Invention

The base end surface is disposed outside the electrode when the center pipe is inserted into the electrode. Thus, the base end surface can contact the base portion remotely from the electrode. The contact piece of the center pipe energizes the electrode by being in contact with the internal circumferential surface of the electrode in the present invention. Therefore, a structure for connecting the base end side cylindrical portion of the electrode and the internal circumferential surface of the electrode seat as described above is made unnecessary. As a result, the structure of the electrode or of the electrode seat can be simplified. Moreover, the electrode can be attached and detached easily without a specialized tool by making the abovementioned thread structure unnecessary. Furthermore, replacement of the torch body is unnecessary even when an energization fault occurs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view along the center axis of a plasma torch according to a first embodiment.

FIG. 2 is an exploded view of the plasma torch.

FIG. 3 is a side view of a replacement part unit.

FIG. 4 is a cross-sectional view along the center axis of the replacement part unit.

FIG. 5 is a perspective view of an electrode.

FIG. 6 is a perspective view of the electrode.

FIG. 7 is a cross-sectional view of the electrode.

FIG. 8 is a perspective view of an insulation guide.

FIG. 9 is a perspective view of the insulation guide.

FIG. 10 is a cross-sectional view of the insulation guide.

FIG. 11 is a view of the insulation guide as seen from the base end side.

FIG. 12 is a cross-sectional view of the insulation guide including the axis of a communication channel.

FIG. 13 is a perspective view of a nozzle.

FIG. 14 is a perspective view of the nozzle.

FIG. 15 is a cross-sectional view of the nozzle.

FIG. 16 is a perspective view of an insulation ring.

FIG. 17 is a perspective view of the insulation ring.

FIG. 18 is a cross-sectional view of the insulation ring.

FIG. 19 is a perspective view of a shield cap.

FIG. 20 is a perspective view of the shield cap.

FIG. 21 is a cross-sectional view of the shield cap.

FIG. 22 is a cross-sectional view along line A-A in FIG. 21.

FIG. 23 is a perspective view of a center pipe.

FIG. 24 is a perspective view of the center pipe.

FIG. 25 is a cross-sectional view of the center pipe.

FIG. 26 is a perspective view of a pipe body.

FIG. 27 is a perspective view of a contact piece.

FIG. 28 is a view of the contact piece as seen from the axial direction.

FIG. 29 is an enlarged view of the replacement part unit in FIG. 1 and the configuration of the vicinity of the same.

FIG. 30 is a cross-sectional view different from FIG. 1 along the center axis of a plasma torch.

FIG. 31 is an enlarged view of the replacement part unit in FIG. 30 and a configuration of the vicinity of the same.

FIG. 32 is a cross-sectional view along the center axis of a plasma torch according to a second embodiment.

FIG. 33 is a cross-sectional view of a replacement part unit according to the second embodiment.

FIG. 34 is a perspective view of the replacement part unit according to the second embodiment.

FIG. 35 is a perspective view of the replacement part unit according to the second embodiment.

FIG. 36 is a perspective view of the nozzle according to the second embodiment.

FIG. 37 is a perspective view of the nozzle according to the second embodiment.

FIG. 38 is a cross-sectional view along the center axis of a plasma torch according to another embodiment.

DETAILED DESCRIPTION OF EMBODIMENT(S) First Embodiment Plasma Torch Configuration

A plasma torch according to the embodiments will be discussed below with reference to the drawings. FIG. 1 is a cross-sectional view along the center axis of a plasma torch 1 a according to a first embodiment. FIG. 2 is an exploded view of the plasma torch 1 a . The plasma torch 1 a according to the present embodiment is a plasma torch 1 a for oxygen plasma cutting. However, the plasma torch 1 a may be a plasma torch for plasma cutting using a gas that does not include oxygen such as nitrogen or argon.

As illustrated in FIG. 2, the plasma torch 1 a includes a replacement part unit 2 a, a torch body 3, a first retainer cap 4 and a second retainer cap 5. The replacement part unit 2 a, the first retainer cap 4, and the second retainer cap 5 are disposed concentrically on the center axis of the torch body 3.

As illustrated in FIG. 1, the replacement part unit 2 a is attached to the torch body 3. The replacement part unit 2 a includes an electrode 6, an insulation guide 7, a nozzle 8, an insulation ring 9, and a shield cap 10. Details of the replacement part unit 2 a are explained below.

The torch body 3 is attached to a connecting pipe 32 via a fixing ring 31. The torch body 3 includes a base portion 33, an electrode seat 34, a center pipe 20, a nozzle seat 36, an insulation sleeve 37, and a holder 38. The base portion 33, the electrode seat 34, the center pipe 20, the nozzle seat 36, the insulation sleeve 37, and the holder 38 are disposed concentrically with the center axis of the torch body 3.

The base portion 33 has a cylindrical shape. The base portion 33 is formed with an electrically conductive body. The center pipe 20, the electrode seat 34, and the insulation sleeve 37 are inserted into a hole of the base portion 33. The electrode seat 34 has a cylindrical shape. The electrode seat 34 is formed with an electrically conductive body. The base portion 33 is electrically connected to a cable from a power source that is not illustrated in the drawings.

The center pipe 20 is inserted into a hole of the electrode seat 34. The center pipe 20 has a tube-like shape. The center pipe 20 is formed with an electrically conductive body. The tip end of the center pipe 20 protrudes from the tip end of the nozzle seat 36. The center pipe 20 is explained in detail below.

The insulation sleeve 37 has a cylindrical shape. The insulation sleeve 37 is formed with an electrically conductive body. A portion of the insulation sleeve 37 is disposed inside the hole of the base portion 33. The insulation sleeve 37 is positioned between the electrode seat 34 and the nozzle seat 36.

The nozzle seat 36 has a cylindrical shape. A tip end portion of the nozzle seat 36 has a tapered shape. The nozzle seat 36 is formed with an insulating body. A contact piece (not illustrated) which electrically contacts the nozzle is attached to the nozzle seat 36. The contact piece is electrically connected to the cable from the power source. The base portion 33 is inserted into a hole of the nozzle seat 36. The insulation sleeve 37 is inserted into the hole of the nozzle seat 36. A tip end portion of the insulation sleeve 37 protrudes from the base portion 33 and is disposed inside the hole of the nozzle seat 36.

The holder 38 has a cylindrical shape. The holder 38 is attached to the connecting pipe 32 by a means such as adhesion. The nozzle seat 36 is inserted into a hole of the holder 38. The tip end portion of the nozzle seat 36 protrudes from the holder 38.

The first retainer cap 4 has a cylindrical shape in which the tip end portion is tapered. The first retainer cap 4 is attached to the torch body 3 so as to cover the nozzle seat 36. The tip end portion of the first retainer cap 4 includes an opening 41 into which the shield cap 10 is inserted. The holder 38 and the nozzle seat 36 are disposed inside the first retainer cap 4. The external circumferential surface of the holder 38 is provided with a male thread portion 311. A female thread portion 42 is provided on the internal circumferential surface of the base end portion of the first retainer cap 4. The first retainer cap 4 is attached to the torch body 3 by screwing the male thread portion 311 of the holder 38 onto the female thread portion 42 of the first retainer cap 4.

The second retainer cap 5 has a cylindrical shape in which the tip end portion is tapered. The tip end portion of the second retainer cap 5 includes an opening 51 into which the shield cap 10 is inserted. The second retainer cap 5 is attached to the first retainer cap 4 so as to cover the first retainer cap 4. The first retainer cap 4 is disposed inside the second retainer cap 5. The first retainer cap 4 and the second retainer cap 5 clamp and hold the replacement part unit 2 a. An O-ring R1 is disposed on the external circumferential surface of the first retainer cap 4. A male thread 401 is provided on the external circumferential surface of the first retainer cap 4, and a female thread 501 is provided on the internal circumferential surface of the second retainer cap 5. The second retainer cap 5 is attached to the first retainer cap 4 by screwing the male thread 401 of the first retainer cap 4 onto the female thread 501 of the second retainer cap 5.

1.2 Replacement Part Unit Configuration

The replacement part unit 2 a will be discussed next. FIG. 3 is a side view of the replacement part unit 2 a. FIG. 4 is a cross-sectional view along the center axis of the replacement part unit 2 a.

As illustrated in FIGS. 3 and 4, the replacement part unit 2 a is a unit in which the electrode 6, the insulation guide 7, the nozzle 8, the insulation ring 9, and the shield cap 10 are integrated by press-fitting. The electrode 6, the insulation guide 7, the nozzle 8, the insulation ring 9, and the shield cap 10 are disposed concentrically with each other. Because the replacement part unit 2 a is disposed concentrically with the center axis of the torch body 3, the center axes of the respective electrode 6, the insulation guide 7, the nozzle 8, the insulation ring 9, and the shield cap 10 match the center axis of the torch body 3.

FIGS. 5 and 6 are perspective views of the electrode 6. FIG. 7 is a cross-sectional view of the electrode 6. As illustrated in FIGS. 5 and 6, the electrode 6 has a cylindrical shape. The electrode 6 is formed with an electrically conductive body. The electrode 6 includes an electrode body portion 61, a coupling portion 62, and a flange portion 63.

The electrode body portion 61 includes the tip end of the electrode 6. A heat resistant insert 64 is embedded in the middle of a tip end surface 602 of the electrode 6. The heat resistant insert 64 is made, for example, from hafnium in the present embodiment. However, an electrode material other than hafnium may be used as the heat resistant insert 64. As illustrated in FIG. 4, a portion of the electrode body portion 61 is disposed inside a hole of the insulation guide 7. The tip end portion of the electrode body portion 61 protrudes from the insulation guide 7. The tip end portion of the electrode body portion 61 has a tapered shape.

The coupling portion 62 is positioned on the base end side of the electrode body portion 61. The coupling portion 62 is positioned between the electrode body portion 61 and the flange portion 63 in the axial direction of the electrode 6. The coupling portion 62 is coupled to the insulation guide 7 by press-fitting. Therefore, the coupling portion 62 is coupled to the insulation guide 7 so as to seal a fluid without an O-ring.

The external circumferential surface of the coupling portion 62 has an uneven shape that engages with the internal circumferential surface of the insulation guide 7. Specifically, the coupling portion 62 includes a protruding portion 621. The protruding portion 621 protrudes from the external circumferential surface of the coupling portion 62. The protruding portion 621 extends in the circumferential direction of the coupling portion 62.

The flange portion 63 is positioned on the base end side of the coupling portion 62. The flange portion 63 includes the base end of the electrode 6. The flange portion 63 has an outer diameter greater than that of the coupling portion 62. The flange portion 63 is longer than the coupling portion 62 in the axial direction of the electrode 6. The external circumferential surface of the flange portion 63 extends in the axial direction of the electrode 6. The external circumferential surface of the flange portion 63 has a flat shape without unevenness as seen in the cross sectional view. Chamfering is performed on the base end portion of the external circumferential surface of the flange portion 63. A step portion 66 is provided between the flange portion 63 and the coupling portion 62. The step portion 66 is a surface perpendicular to the axial direction of the electrode 6.

The electrode 6 includes an internal channel 65. The center pipe 20 illustrated in FIG. 1 is inserted into the internal channel 65. An inlet of the internal channel 65 is provided on a base end surface 601 of the electrode 6. The internal channel 65 extends in the axial direction of the electrode 6 from the base end surface 601 toward the tip end of the electrode 6. A protruding portion 67 is provided on the side 6 f the internal channel 65 at the tip end of the electrode 6. The abovementioned heat resistant insert 64 is disposed inside the protruding portion 67. A portion of the protruding portion 67 is disposed inside a cooling water channel of the center pipe 20 while the replacement part unit 2 a is attached to the torch body 3.

The internal circumferential surface of the internal channel 65 includes a linear portion 651 and a tapered portion 652. The linear portion 651 extends parallel to the axial direction of the electrode 6. The tapered portion 652 expands in the radial direction toward the inlet of the internal channel 65.

The insulation guide 7 will be discussed next. FIGS. 8 and 9 are perspective views of the insulation guide 7. FIG. 10 is a cross-sectional view of the insulation guide 7. The insulation guide 7 electrically insulates the electrode 6 and the nozzle 8 and couples the electrode 6 and the nozzle 8. The insulation guide 7 positions the electrode 6 and the nozzle 8 in the axial direction and the radial direction with regard to each other.

The insulation guide 7 has a tubular shape. The insulation guide 7 is formed with an insulating body. The insulation guide 7 includes a hole 706 into which the electrode 6 is inserted. The hole 706 of the insulation guide 7 penetrates the insulation guide 7 in the axial direction of the insulation guide 7.

The insulation guide 7 is formed with a material having a modulus of elasticity that is less than the modulus of elasticity of a ceramic. The insulation guide 7 is made from a resin such as an engineered plastic in the present embodiment. Specifically, the insulation guide 7 is made from a resin that has a continuous use temperature of 100° C. or higher. Moreover, the insulation guide 7 is preferably made from a resin that has a continuous use temperature of 300° C. or less. However, the insulation guide 7 may be made from a material other than a resin.

As illustrated in FIG. 10, the internal circumferential surface of the insulation guide 7 includes a first internal circumferential surface 71, an inside step portion 72, and a second internal circumferential surface 73. The first internal circumferential surface 71 extends in the axial direction of the insulation guide 7 and reaches a tip end surface 701 of the insulation guide 7. The first internal circumferential surface 71 has an inner diameter that is greater than that of the second internal circumferential surface 73. The first internal circumferential surface 71 faces the external circumferential surface of the electrode body portion 61 with a gap therebetween. As explained below, the first internal circumferential surface 71 configures a gas channel with the external circumferential surface of the electrode body portion 61. The inner diameter of the first internal circumferential surface 71 is roughly the same as the inner diameter of the nozzle 8. Therefore, the inner diameter of the gas channel between the first internal circumferential surface 71 and the electrode 6 is roughly the same as the inner diameter of the nozzle 8.

The inside step portion 72 is positioned on the base end side of the first internal circumferential surface 71. The inside step portion 72 is positioned between the first internal circumferential surface 71 and the second internal circumferential surface 73 in the axial direction of the insulation guide 7. The inside step portion 72 is inclined with respect to the axial direction of the insulation guide 7 so as to become larger in the radial direction toward the tip end side.

A heat resistant coating 707 is formed on the first internal circumferential surface 71 and the inside step portion 72. The heat resistant coating 707 is formed from a ceramic-based material. The heat resistant coating 707 is formed from boron nitride for example. However, the heat resistant coating 707 may be formed from a ceramic-based material other than boron nitride. Alternatively, the heat resistant coating 707 may be formed from a heat resistant material other than a ceramic-based material. Alternatively, the heat resistant coating 707 may be omitted.

The second internal circumferential surface 73 is positioned on the base end side of the inside step portion 72. The second internal circumferential surface 73 extends in the axial direction of the insulation guide 7 and reaches a base end surface 702 of the insulation guide 7. The second internal circumferential surface 73 includes a first coupling portion 74. The first coupling portion 74 is coupled to the coupling portion 62 of the electrode 6 by press-fitting. Therefore, the first coupling portion 74 of the insulation guide 7 is coupled to the electrode 6 so as to seal a fluid without an O-ring.

As illustrated in FIG. 4, the electrode 6 and the insulation guide 7 are positioned in the radial direction with respect to each other due to the first coupling portion 74 of the insulation guide 7 being coupled with the coupling portion 62 of the electrode 6. Moreover, the base end surface 702 of the insulation guide 7 comes into contact with the step portion 66 of the flange portion 63 of the electrode 6 whereby the electrode 6 and the insulation guide 7 are positioned in the axial direction with respect to each other.

The first coupling portion 74 has an uneven shape that engages with the external circumferential surface of the electrode 6. Specifically, the first coupling portion 74 includes a protruding portion 741. The protruding portion 741 protrudes from the second internal circumferential surface 73. The protruding portion 741 extends in the circumferential direction of the second internal circumferential surface 73. The protruding portion 741 of the first coupling portion 74 of the insulation guide 7 engages with the protruding portion 621 of the coupling portion 62 of the electrode 6. As a result, the insulation guide 7 is securely locked onto the electrode 6.

The external circumferential surface of the insulation guide 7 includes a first external circumferential surface 75, a second external circumferential surface 76, and a third external circumferential surface 77. The first external circumferential surface 75 extends in the axial direction of the insulation guide 7 and reaches the tip end surface 701 of the insulation guide 7. The first external circumferential surface 75 is disposed inside a first hole 811 of the nozzle 8. The first external circumferential surface 75 includes a second coupling portion 78. The second coupling portion 78 is coupled to the internal circumferential surface of the nozzle 8 by press-fitting. Therefore, the second coupling portion 78 of the insulation guide 7 is coupled to the nozzle 8 so as to seal a fluid without an O-ring.

The second coupling portion 78 of the insulation guide 7 has an uneven shape that engages with the internal circumferential surface of the nozzle 8. Specifically, the second coupling portion 78 of the insulation guide 7 includes a protruding portion 781. The protruding portion 781 protrudes from the first external circumferential surface 75. The protruding portion 781 extends in the circumferential direction of the first external circumferential surface 75.

The second external circumferential surface 76 is positioned on the base end side of the first external circumferential surface 75. The second external circumferential surface 76 extends in the axial direction of the insulation guide 7. The second external circumferential surface 76 has a flat shape without unevenness as seen in the cross sectional view. The second external circumferential surface 76 is disposed between the first external circumferential surface 75 and the third external circumferential surface 77 in the axial direction of the insulation guide 7. The second external circumferential surface 76 is disposed outside of the nozzle 8. The second external circumferential surface 76 has an outer diameter that is smaller than that of the first external circumferential surface 75. In other words, the outer diameter of the first external circumferential surface 75 is greater than the outer diameter of the second external circumferential surface 76. The first external circumferential surface 75 is shorter than the second external circumferential surface 76 in the axial direction of the insulation guide 7.

The third external circumferential surface 77 is positioned on the base end side of the second external circumferential surface 76. The third external circumferential surface 77 has an outer diameter that is smaller than that of the second external circumferential surface 76. The third external circumferential surface 77 extends in the axial direction of the insulation guide 7 and reaches the base end surface 702 of the insulation guide 7. The second external circumferential surface 76 is longer than the third external circumferential surface 77 in the axial direction of the insulation guide 7. In other words, the third external circumferential surface 77 is shorter than the second external circumferential surface 76 in the axial direction of the insulation guide 7. The third external circumferential surface 77 is shorter than the first external circumferential surface 75 in the axial direction of the insulation guide 7.

The external circumferential surface of the insulation guide 7 includes an outside step portion 79. The outside step portion 79 is disposed between the second external circumferential surface 76 and the third external circumferential surface 77. The outside step portion 79 is a surface perpendicular to the axial direction of the insulation guide 7.

FIG. 11 is a view of the insulation guide 7 seen from the base end side. As illustrated in FIGS. 9 and 11, the insulation guide 7 includes a plurality of communication channels 703. The insulation guide 7 includes six communication channels 703 in the present embodiment. The number of communication channels 703 is not limited to six and may be less than six or greater than six.

FIG. 12 is a cross-sectional view of the insulation guide 7 including the axis of one of the communication channels 703. As illustrated in FIG. 12, the communication channels 703 allow communication between the outside of the insulation guide 7 and the inside of the hole 706 of the insulation guide 7. In other words, the communication channels 703 allow communication between the outside of the insulation guide 7 and the gas channel inside the insulation guide 7. The communication channels 703 extend in a direction inclined with respect to the axial direction. The communication channels 703 are inclined so as to approach the axis of the insulation guide 7 toward the tip end of the insulation guide 7. The inclination angle of the communication channels 703 with respect to the axial direction of the insulation guide 7 is preferably at least 30 degrees and no greater than 60 degrees. For example, the inclination angle of the communication channels 703 with respect to the axial direction of the insulation guide 7 is 45 degrees.

One end of each of the communication channels 703 is connected to the inside step portion 72. The other end of each of the communication channels 703 is connected to the outside step portion 79. Each communication channel 703 is connected to the external circumferential surface of the insulation guide 7 at a position nearer the base end side than the center in the axial direction of the insulation guide 7. Each communication channel 703 has a first communication channel 704 and a second communication channel 705.

The first communication channel 704 has a larger flow path cross-section than the second communication channel 705. The first communication channel 704 is connected to the outside step portion 79. The first communication channel 704 communicates with the outside of the insulation guide 7. The second communication channel 705 is connected to the inside step portion 72. The second communication channel 705 communicates with the gas channel inside the insulation guide 7. While only one communication channel 703 is illustrated in FIG. 12, the other communication channels 703 have the same structure as the communication channel 703 in FIG. 12.

As illustrated in FIG. 11, the plurality of communication channels 703 are inclined with respect to the circumferential direction and the radial direction. All of the communication channels 703 are inclined in the same direction with respect to the circumferential direction. All of the communication channels 703 are inclined in the same direction with respect to the radial direction. As a result, gas emitted from the communication channels 703 produces a swirling flow. The plurality of communication channels 703 are disposed at equal intervals in the circumferential direction of the insulation guide 7. The axis of each communication channel 703 is separated by a predetermined distance from a straight line parallel to the axis of each communication channel 703 and passing through the center of the insulation guide 7.

The nozzle 8 will be discussed next. FIGS. 13 and 14 are perspective views of the nozzle 8. FIG. 15 is a cross-sectional view of the nozzle 8. The nozzle 8 has a cylindrical shape in which the tip end portion is tapered. The nozzle 8 includes a hole 811 into which the insulation guide 7 is inserted and the nozzle 8 is coupled to the insulation guide 7 by press-fitting. Specifically, the nozzle 8 includes a first nozzle portion 81, a second nozzle portion 82, and a third nozzle portion 83.

The first nozzle portion 81 includes the base end of the nozzle 8. The first nozzle portion 81 includes the first hole 811. The second nozzle portion 82 is positioned on the tip end side of the first nozzle portion 81. The second nozzle portion 82 is positioned between the first nozzle portion 81 and the third nozzle portion 83 in the axial direction of the nozzle 8. The second nozzle portion 82 is longer than the first nozzle portion 81 in the axial direction of the nozzle 8.

The second nozzle portion 82 includes a second hole 821 that communicates with the first hole 811. The second hole 821 has an internal diameter that is smaller than that of the first hole 811. Therefore, an inside step portion 84 is provided between an internal circumferential surface 812 of the first nozzle portion 81 and an internal circumferential surface 822 of the second nozzle portion 82. The inside step portion 84 is a surface perpendicular to the axial direction of the nozzle 8.

The outer diameter of the second nozzle portion 82 is the same as the outer diameter of the first nozzle portion 81. Therefore, an external circumferential surface 823 of the second nozzle portion 82 is flush with an external circumferential surface 813 of the first nozzle portion 81. Chamfering is performed on the base end of the external circumferential surface 813 of the first nozzle portion 81. The second nozzle portion 82 has a thickness in the radial direction that is larger than that of the first nozzle portion 81.

The third nozzle portion 83 includes the tip end of the nozzle 8. The third nozzle portion 83 is positioned on the tip end side of the second nozzle portion 82. The third nozzle portion 83 includes a jetting hole 831. The jetting hole 831 has an internal diameter that is smaller than that of the second hole 821. The jetting hole 831 extends in the axial direction of the nozzle 8 and reaches a tip end surface 801 of the nozzle 8. The abovementioned first hole 811 is shorter than the jetting hole 831 in the axial direction of the nozzle 8.

The jetting hole 831 communicates with the second hole 821 via a tapered hole 832. The tapered hole 832 is positioned between the jetting hole 831 and the second hole 821 in the axial direction of the nozzle 8 and is connected to the jetting hole 831 and the second hole 821. The tapered hole 832 decreases in size in the radial direction toward the tip end of the nozzle 8.

The external circumferential surface of the nozzle 8 includes a first external circumferential surface 85, a second external circumferential surface 86, and a third external circumferential surface 87. The first external circumferential surface 85 reaches a base end surface 802 of the nozzle 8. The first external circumferential surface 85 is configured by the external circumferential surface 813 of the first nozzle portion 81 and the external circumferential surface 823 of the second nozzle portion 82. The first external circumferential surface 85 has a linear shape that extends in the axial direction of the nozzle 8 as seen in the cross sectional view. In other words, the first external circumferential surface 85 has a flat shape without unevenness as seen in the cross sectional view.

The second external circumferential surface 86 is positioned on the tip end side of the first external circumferential surface 85. The second external circumferential surface 86 is positioned between the first external circumferential surface 85 and the third external circumferential surface 87 in the axial direction of the nozzle 8. The second external circumferential surface 86 has an outer diameter that is smaller than that of the first external circumferential surface 85. Therefore, an outside step portion 88 is provided between the first external circumferential surface 85 and the second external circumferential surface 86. The outside step portion 88 is a surface perpendicular to the axial direction of the nozzle 8.

The third external circumferential surface 87 is positioned on the tip end side of the second external circumferential surface 86. The third external circumferential surface 87 reaches the tip end surface 801 of the nozzle 8. The third external circumferential surface 87 is inclined so as to become smaller in the radial direction toward the tip end.

The insulation guide 7 is inserted into the first hole 811 of the first nozzle portion 81. The electrode 6 is inserted into the second hole 821 of the second nozzle portion 82. As illustrated in FIG. 4, the internal circumferential surface 822 of the second nozzle portion 82 faces the electrode body portion 61 with a gap therebetween. The tip end of the electrode 6 faces the tapered hole 832 of the third nozzle portion 83.

The first nozzle portion 81 is coupled to the insulation guide 7. Specifically, the second coupling portion 78 of the insulation guide 7 is inserted into the first hole 811, and the first nozzle portion 81 is coupled to the second coupling portion 78 of the insulation guide 7 by press-fitting. As a result, the internal circumferential surface 812 of the first nozzle portion 81 is coupled to the insulation guide 7 so as to seal a fluid without an O-ring.

The internal circumferential surface 812 of the first nozzle portion 81 is coupled to the second coupling portion 78 of the insulation guide 7 whereby the nozzle 8 and the insulation guide 7 are positioned in the radial direction with regard to each other. Further, the tip end surface 701 of the insulation guide 7 comes into contact with the inside step portion 84 of the nozzle 8 whereby the nozzle 8 and the insulation guide 7 are positioned in the axial direction with regard to each other.

The internal circumferential surface 812 of the first nozzle portion 81 has an uneven shape that engages with the external circumferential surface of the insulation guide 7. Specifically, the internal circumferential surface 812 of the first nozzle portion 81 includes a protruding portion 814. The protruding portion 814 of the first nozzle portion 81 engages with the protruding portion 781 of the second coupling portion 78 of the insulation guide 7. As a result, the nozzle 8 is locked onto the insulation guide 7.

The second external circumferential surface 86 has an uneven shape that engages with the internal circumferential surface of the insulation ring 9. Specifically, the second external circumferential surface 86 includes a protruding portion 861.

FIGS. 16 and 17 are perspective views of the insulation ring 9. FIG. 18 is a cross-sectional view of the insulation ring 9. As illustrated in FIGS. 16 to 18, the insulation ring 9 includes a hole 903 into which the nozzle 8 is inserted. An internal circumferential surface 91 of the insulation ring 9 includes a protruding portion 911. An external circumferential surface 92 of the insulation ring 9 includes a protruding portion 921.

The insulation ring 9 includes a flange portion 93. The flange portion 93 protrudes from the external circumferential surface 92 of the insulation ring 9. Therefore, a step portion 94 is provided between the external circumferential surface 92 and the flange portion 93 of the insulation ring 9. The step portion 94 is a surface perpendicular to the axial direction of the insulation ring 9.

As illustrated in FIG. 4, the insulation ring 9 is coupled to the nozzle 8 by press-fitting. Specifically, the internal circumferential surface 91 of the insulation ring 9 is coupled to the second external circumferential surface 86 of the nozzle 8 by press-fitting. The internal circumferential surface 91 of the insulation ring 9 is coupled to the second external circumferential surface 86 of the nozzle 8 whereby the insulation ring 9 and the nozzle 8 are positioned in the radial direction with regard to each other.

Further, a base end surface 901 of the insulation ring 9 comes into contact with an outside end portion 88 of the nozzle 8, whereby the insulation ring 9 and the nozzle 8 are positioned in the axial direction with regard to each other. The protruding portion 911 of the internal circumferential surface 91 of the insulation ring 9 engages with the protruding portion 861 of the second external circumferential surface 86 of the nozzle 8. As a result, the insulation ring 9 is securely locked onto the nozzle 8.

FIGS. 19 and 20 are perspective views of the shield cap 10. FIG. 21 is a cross-sectional view of the shield cap 10. As illustrated in FIGS. 19 to 21, the shield cap 10 includes a hole 103. The nozzle 8 is inserted into the hole 103 of the shield cap 10. The shield cap 10 includes a jetting hole 104. The jetting hole 104 communicates with the hole 103 and passes through a tip end surface 101 of the shield cap 10 in the axial direction.

The shield cap 10 includes a first internal circumferential surface 11 and a second internal circumferential surface 12. The first internal circumferential surface 11 extends in the axial direction of the shield cap 10 and reaches a base end surface 102 of the shield cap 10. The first internal circumferential surface 11 includes a protruding portion 111. The second internal circumferential surface 12 is positioned on the tip end side of the first internal circumferential surface 11. The second internal circumferential surface 12 is inclined so as to become smaller in the radial direction toward the tip end.

The shield cap 10 includes a first external circumferential surface 13, a flange portion 14, a second external circumferential surface 15, and a third external circumferential surface 16. The first external circumferential surface 13 extends in the axial direction of the shield cap 10 and reaches the base end surface 102 of the shield cap 10. The flange portion 14 is positioned on the tip end side of the first external circumferential surface 13. The flange portion 14 is positioned between the first external circumferential surface 13 and the second external circumferential surface 15 in the axial direction of the shield cap 10. The flange portion 14 protrudes from the first external circumferential surface 13. The flange portion 14 protrudes from the second external circumferential surface 15. An outside step portion 17 is provided between the flange portion 14 and the second external circumferential surface 15. The outside step portion 17 is a surface perpendicular to the axial direction of the shield cap 10. The outer diameter of the flange portion 14 is greater than the diameter of the opening 41 of the first retainer cap 4. The outer diameter of the flange portion 14 is greater than the diameter of the opening 51 of the second retainer cap 5.

The second external circumferential surface 15 is positioned on the tip end side of the flange portion 14. The second external circumferential surface 15 has an outer diameter that is smaller than that of the first external circumferential surface 13. The second external circumferential surface 15 extends in the axial direction of the shield cap 10. The third external circumferential surface 16 is positioned on the tip end side of the second external circumferential surface 15. The third external circumferential surface 16 reaches the tip end surface 101 of the shield cap 10. The third external circumferential surface 16 is inclined with respect to the axial direction of the shield cap 10 so as to become smaller in the radial direction toward the tip end.

FIG. 22 depicts the cross-sectional view A-A in FIG. 21. As illustrated in FIGS. 21 and 22, the shield cap 10 includes a plurality of communication channels 105. The communication channels 105 allow communication between the outside of the shield cap 10 and the inside of the hole 103 of the shield cap 10. One end of each of the communication channels 105 reaches the first external circumferential surface 13. The other end of each of the communication channels 105 reaches the first internal circumferential surface 11.

The communication channels 105 are disposed in equal intervals in the circumferential direction of the shield cap 10. The axis of each communication channel 105 is separated by a predetermined distance from a straight line parallel to the axis of each communication channel 105 and passing through the center of the insulation guide 7 as seen in the axial direction of the shield cap 10. All of the communication channels 105 are inclined in the same direction with respect to the circumferential direction. All of the communication channels 105 are inclined in the same direction with respect to the radial direction. As a result, gas emitted from the communication channels 105 produces a swirling flow.

As illustrated in FIG. 4, the shield cap 10 is coupled to the insulation ring 9 by press-fitting. Specifically, the first internal circumferential surface 11 of the shield cap 10 is coupled to the external circumferential surface 92 of the insulation ring 9 by press-fitting. The protruding portion 111 of the first internal circumferential surface 11 of the shield cap 10 is engaged with the protruding portion 921 of the external circumferential surface 92 of the insulation ring 9. As a result, the shield cap 10 is securely locked onto the insulation ring 9.

The first internal circumferential surface 11 of the shield cap 10 is coupled to the external circumferential surface 92 of the insulation ring 9 whereby the shield cap 10 and the insulation ring 9 are positioned in the radial direction with respect to each other. As a result, the jetting hole 104 of the shield cap 10 and the jetting hole 831 of the nozzle 8 are disposed concentrically.

The base end surface 102 of the shield cap 10 comes into contact with the step portion 94 of the insulation ring 9 whereby the shield cap 10 and the insulation ring 9 are positioned in the axial direction with respect to each other. As a result, the shield cap 10 is disposed so as to be spaced away from the nozzle 8 with a gap therebetween. Specifically, the second internal circumferential surface 12 of the shield cap 10 is disposed so as to be spaced away from the third external circumferential surface 87 of the nozzle 8 with a gap therebetween. As a result, the belowmentioned gas channel is configured between the shield cap 10 and the nozzle 8. The communication channels 105 of the shield cap 10 are positioned closer to the tip end side than the tip end of the insulation ring 9. The communication channels 105 of the shield cap 10 communicate with the gas channel between the shield cap 10 and the nozzle 8.

The center pipe 20 will be discussed next. FIGS. 23 and 24 are perspective views of the center pipe 20. FIG. 25 is a cross-sectional view of the center pipe 20. The center pipe 20 is inserted into the internal channel 65 of the electrode 6 and supplies cooling water into the electrode 6. The center pipe 20 is formed with an electrically conductive body. The center pipe 20 includes a pipe body 21 and a contact piece 22. FIG. 26 is a perspective view of the pipe body 21. FIG. 27 is a perspective view of the contact piece 22.

The pipe body 21 has a tube-like shape. The pipe body 21 is formed from an electrically conductive body. Specifically, the external circumferential surface of the pipe body 21 includes a flange portion 23, a first external circumferential surface 24, a second external circumferential surface 25, and a third external circumferential surface 26. The flange portion 23 includes the base end of the pipe body 21. The flange portion 23 protrudes from the first external circumferential surface 24. Therefore, a step portion 27 is provided between the flange portion 23 and the first external circumferential surface 24. The step portion 27 is a surface perpendicular to the axial direction of the pipe body 21.

The first external circumferential surface 24 is positioned on the tip end side of the flange portion 23. The first external circumferential surface 24 is positioned between the flange portion 23 and the second external circumferential surface 25 in the axial direction of the pipe body 21. The first external circumferential surface 24 extends in the axial direction of the pipe body 21.

The second external circumferential surface 25 is positioned on the tip end side of the first external circumferential surface 24. The second external circumferential surface 25 is positioned between the first external circumferential surface 24 and the third external circumferential surface 26 in the axial direction of the pipe body 21. The second external circumferential surface 25 extends in the axial direction of the pipe body 21. The second external circumferential surface 25 is shorter than the first external circumferential surface 24 in the axial direction of the pipe body 21. The second external circumferential surface 25 has an outer diameter that is smaller than that of the first external circumferential surface 24.

The third external circumferential surface 26 is positioned on the tip end side of the second external circumferential surface 25. The third external circumferential surface 26 includes the tip end of the pipe body 21. The third external circumferential surface 26 extends in the axial direction of the pipe body 21. The third external circumferential surface 26 is longer than the first external circumferential surface 24 in the axial direction of the pipe body 21. The third external circumferential surface 26 has an outer diameter that is smaller than that of the second external circumferential surface 25. A recessed portion 261 is provided in the intermediate portion in the axial direction of the third external circumferential surface 26. The contact piece 22 is attached to the recessed portion 261.

The pipe body 21 includes a cooling water channel on the inside thereof. The cooling water channel passes through the pipe body 21 in the axial direction. The cooling water channel includes a first channel 211, a second channel 212, and a third channel 231. The first channel 211 reaches a base end surface 201 of the pipe body 21. The first channel 211 is inclined with respect to the axial direction of the pipe body 21 so as to become smaller in the radial direction toward the tip end.

The second channel 212 is positioned on the tip end side of the first channel 211. The second channel 212 is positioned between the first channel 211 and the third channel 231 in the axial direction of the pipe body 21. The second channel 212 is longer than the third channel 231 in the axial direction of the pipe body 21. The second channel 212 extends in the axial direction of the pipe body 21.

The third channel 231 is positioned on the tip end side of the second channel 212. The third channel 231 reaches a tip end surface 202 of the pipe body 21. The third channel 231 has an inner diameter that is greater than that of the second channel 212. The abovementioned protruding portion 67 of the electrode 6 is disposed inside the third channel 231.

The contact piece 22 is separate from the pipe body 21. The contact piece 22 is formed from an electrically conductive body. The contact piece 22 is attached in a detachable manner to the pipe body 21. The contact piece 22 is attached to the external circumferential surface of the pipe body 21. Specifically, the contact piece 22 is attached to the pipe body 21 by being fitted into the recessed portion 261 of the third external circumferential surface 26 of the pipe body 21.

The contact piece 22 includes an attachment portion 28 and a contact portion 29. The attachment portion 28 is attached to the external circumferential surface of the pipe body 21. The attachment portion 28 includes a first ring portion 281 and a second ring portion 282. The second ring portion 282 is disposed away from the first ring portion 281 in the axial direction of the contact piece 22. The first ring portion 281 and the second ring portion 282 are both fitted into the recessed portion 261 of the pipe body 21.

The contact portion 29 comes into contact with the internal circumferential surface of the electrode 6. The contact portion 29 has elasticity to produce a counterforce when pressed in the radial direction of the contact piece 22. Specifically, the contact portion 29 includes a plurality of curved portions 291. The curved portions 291 are coupled to the first ring portion 281 and the second ring portion 282. The curved portions 291 have a plate-like shape that bulges outward in the radial direction of the contact piece 22. The contact portion 29 includes a plurality of slits 292. The slits 292 are provided between the plurality of curved portions 291 and extend in the axial direction of the contact piece 22. Only a portion of the slits 292 are given the reference numeral 292 in the drawings and the reference numerals of the other slits 292 s are omitted.

FIG. 28 is a view of the contact piece 22 as seen from the axial direction. As illustrated in FIG. 28, the plurality of curved portions 291 are disposed at equal intervals in the circumferential direction of the contact piece 22. The plurality of slits 292 are similarly disposed at equal intervals in the circumferential direction of the contact piece 22. The contact piece 22 includes eight curved portions 291 and eight slits 292 in the present embodiment. However, the number of curved portions 291 is not limited to eight, and may be less than eight or more than eight. Similarly, the number of slits 292 is not limited to eight, and may be less than eight or more than eight.

As illustrated in FIG. 1, the flange portion of the center pipe 20 is disposed between a base end surface 341 of the electrode seat 34, and a bottom surface 331 of the hole of the base portion 33. The flange portion 23 comes into contact with the base end surface 341 of the electrode seat 34. As a result, the center pipe 20 and the electrode seat 34 are electrically connected. Moreover, the center pipe 20 is positioned in the radial direction and the axial direction.

FIG. 29 is an enlarged view of the replacement part unit 2 a in FIG. 1 and the configuration of the vicinity of the same. As illustrated in FIG. 29, the contact piece 22 of the center pipe 20 comes into contact with the internal circumferential surface of the electrode 6. The contact piece 22 is elastically deformed toward the inside in the radial direction due to the contact piece 22 being inserted into the internal channel 65 of the electrode 6. The contact piece 22 is pressed against the internal circumferential surface of the electrode 6 due to the counterforce of the elastic deformation. The center pipe 20 and the electrode seat 34 are electrically connected. Therefore, the contact piece 22 comes into contact with the internal circumferential surface of the electrode 6 thereby energizing the electrode 6.

The electrode 6 includes a first energization surface 603 and a second energization surface 601. The first energization surface 603 is a portion that is in contact with the contact piece 22 on the internal circumferential surface of the internal channel 65. The electrode 6 is electrically connected with the electrode seat 34 via the center pipe 20 and the first energization surface 603. The first energization surface 603 is disposed adjoining the tapered portion 652 at the tip end side of the tapered portion 652. The first energization surface 603 is positioned inside the belowmentioned cooling water channel.

The second energization surface 601 is the base end surface 601 of the electrode 6. The second energization surface 601 comes into contact with a tip end surface 342 of the electrode seat 34. The electrode 6 is electrically connected with the electrode seat 34 via the second energization surface 601. The second energization surface 601 is adjacent to the belowmentioned cooling water channel.

1.3 Cooling Water Channel

The cooling water channel of the plasma torch 1 a will be discussed next. The solid line arrows in FIG. 1 indicate the flow of the cooling water. As illustrated in FIG. 1, a cooling water supply pipe 45 is connected to the base portion 33. The cooling water supply pipe 45 is connected to a second cooling water channel W2 inside the nozzle seat 36 via a first cooling water channel W1 inside the base portion 33. The first cooling water channel W1 extends from the base end surface of the base portion 33 toward the external circumferential surface of the base portion 33. The second cooling water channel W2 extends from the internal circumferential surface of the nozzle seat 36 toward the tip end portion of the nozzle seat 36. The second cooling water channel W2 is connected to a third cooling water channel W3. The third cooling water channel W3 is an annular channel enclosed by the nozzle seat 36, the first retainer cap 4, and the replacement part unit 2 a.

As illustrated in FIG. 29, a gap is provided between a tip end surface 371 of the insulation sleeve 37 and the base end surface 802 of the nozzle 8, and the gap configures a portion of the third cooling water channel W3. Therefore, the base end surface 802 of the nozzle 8 is disposed inside the third cooling water channel W3. Moreover, the gap between the tip end surface 371 of the insulation sleeve 37 and the base end surface 802 of the nozzle 8 reaches as far as the second external circumferential surface 76 of the insulation guide 7. Therefore, a portion of the second external circumferential surface 76 of the insulation guide 7 is disposed inside the third cooling water channel W3.

As illustrated in FIG. 1, the third cooling water channel W3 is connected to an eighth cooling water channel W8 via a fourth cooling water channel W4 inside the nozzle seat 36, a fifth cooling water channel W5 between the nozzle seat 36 and the insulation sleeve 37, a sixth cooling water channel W6 inside the insulation sleeve 37, and a seventh cooling water channel W7 inside the electrode seat 34.

The fourth cooling water channel W4 extends from the tip end of the nozzle seat 36 toward the internal circumferential surface of the nozzle seat 36. The fifth cooling water channel W5 is an annular channel provided between the nozzle seat 36 and the insulation sleeve 37. The sixth cooling water channel W6 is a plurality of channels extending in the radial direction from the external circumferential surface of the insulation sleeve 37 toward the internal circumferential surface of the insulation sleeve 37. The seventh cooling water channel W7 is a plurality of channels extending in the radial direction from the external circumferential surface of the electrode seat 34 toward the internal circumferential surface of the electrode seat 34. The eighth cooling water channel W8 is a channel between the electrode seat 34 and the center pipe 20.

The eighth cooling water channel W8 is connected to a ninth cooling water channel W9 between the electrode 6 and the center pipe 20. The ninth cooling water channel W9 communicates with a tenth cooling water channel W10 inside the center pipe 20 at the tip end portion of the center pipe 20. The tenth cooling water channel W10 is connected to a cooling water exhaust pipe 46 via an eleventh cooling water channel W11 inside the base portion 33.

The cooling water is supplied from a cooling water supply source, through the cooling water supply pipe 45, the first cooling water channel W1 inside the base portion 33, and the second cooling water channel W2 inside the nozzle seat 36, to the third cooling water channel W3. The cooling water passes from the third cooling water channel W3, through the fourth cooling water channel W4 inside the nozzle seat 36, the fifth cooling water channel W5 between the nozzle seat 36 and the insulation sleeve 37, the sixth cooling water channel W6 inside the insulation sleeve 37, and the seventh cooling water channel W7 inside the electrode seat 34, to the eighth cooling water channel W8 between the electrode seat 34 and the center pipe 20. The cooling water passes from the eighth cooling water channel W8, through the ninth cooling water channel W9 between the electrode 6 and the center pipe 20, the tenth cooling water channel W10 inside the center pipe 20, the eleventh cooling water channel W11 inside the base portion 33, and the cooling water exhaust pipe 46, to be exhausted to the outside of the plasma torch 1 a.

1.4 Gas Channel

The plasma gas channel of the plasma torch 1 a will be discussed next. The plasma gas of the present embodiment is oxygen gas. However, another gas such as argon or nitrogen may be used. FIG. 30 is a cross-sectional view different from FIG. 1 along the center axis of a plasma torch. The dashed line arrows in FIGS. 1 and 30 indicate the flow of the plasma gas. Specifically, the dashed line arrows in FIG. 30 indicate the flow of the main gas. The dashed line arrows in FIG. 1 indicate the flow of the assist gas.

As illustrated in FIG. 30, a main gas supply pipe 47 is connected to the base portion 33. The main gas supply pipe 47 is connected to a second main gas channel MG2 between the base portion 33 and the insulation sleeve 37 via a first main gas channel MG1 inside the base portion 33. The first main gas channel MG1 extends in the axial direction from the base end surface of the base portion 33 toward a step portion 332 of the internal circumferential surface of the base portion 33. The second main gas channel MG2 is an annular channel formed between the step portion 332 of the internal circumferential surface of the base portion 33 and a step portion 372 of the external circumferential surface of the insulation sleeve 37.

The second main gas channel MG2 is connected to a fourth main gas channel MG4 via a third main gas channel MG3 inside the insulation sleeve 37. The third main gas channel MG3 extends in the axial direction from the step portion 372 of the external circumferential surface of the insulation sleeve 37. The fourth main gas channel MG4 is an annular channel between the insulation sleeve 37 and the replacement part unit 2 a.

FIG. 31 is an enlarged view of the replacement part unit 2 a in FIG. 30 and the configuration of the vicinity of the same. As illustrated in FIG. 31, the fourth main gas channel MG4 is configured by the internal circumferential surface of the insulation sleeve 37, the external circumferential surface of the insulation guide 7, and the external circumferential surface of the electrode 6.

Specifically, a step portion 373 is provided on the internal circumferential surface of the insulation sleeve 37. The step portion 373 is a surface perpendicular to the axial direction of the insulation sleeve 37. While the replacement part unit 2 a is attached to the torch body 3, the outside step portion 79 of the insulation guide 7 is disposed away from the step portion 373 in the internal circumferential surface of the insulation sleeve 37 with a gap therebetween. The fourth main gas channel MG4 passes through the gap between the outside step portion 79 of the insulation guide 7 and the step portion 373 of the internal circumferential surface of the insulation sleeve 37.

The fourth main gas channel MG4 is sealed from the abovementioned third cooling water channel W3 by an O-ring R2. The O-ring R2 is fitted into a recessed portion 374 provided on the internal circumferential surface of the insulation sleeve 37. The O-ring R2 comes into contact with a portion of the second external circumferential surface 76 of the insulation guide 7. That is, the second external circumferential surface 67 of the insulation guide 7 has a seal surface 761 that is in contact with the O-ring. A portion of the second external circumferential surface 76 on the tip end side of the seal surface 761 is disposed inside the third cooling water channel W3. A portion of the second external circumferential surface 76 on the base end side of the seal surface 761 is disposed inside the fourth main gas channel MG4. The third external circumferential surface 77 is also disposed inside the fourth main gas channel MG4 in the same way as the second external circumferential surface 76.

As illustrated in FIG. 29, the fourth main gas channel MG4 is sealed from the abovementioned sixth cooling water channel W6 and the seventh cooling water channel W7 by an O-ring R3. The O-ring R3 is fitted into a recessed portion 375 provided on the internal circumferential surface of the insulation sleeve 37. The O-ring R3 comes into contact with a portion of the external circumferential surface of the flange portion 63 of the electrode 6. That is, the external circumferential surface of the flange portion 63 includes a seal surface 631 that comes into contact with the O-ring R3. A portion of the external circumferential surface of the flange portion 63 on the tip end side of the seal surface 631 is disposed inside the fourth main gas channel MG4.

As illustrated in FIG. 31, the fourth main gas channel MG4 is connected to a fifth main gas channel MG5 between the insulation guide 7 and the electrode 6 via the plurality of communication channels 703 of the insulation guide 7. The fifth main gas channel MG5 is an annular channel between the internal circumferential surface of the insulation guide 7 and the external circumferential surface of the electrode 6. The fifth main gas channel MG5 is connected to a sixth main gas channel MG6 between the nozzle 8 and the electrode 6. The inner diameter of the fifth main gas channel MG5 is the same as the inner diameter of the sixth main gas channel MG6. The sixth main gas channel MG6 communicates with the jetting hole 831 of the nozzle 8.

The main gas flows from the main gas supply source, through the first main gas channel MG1 inside the base portion 33, the second main gas channel MG2 between the base portion 33 and the insulation sleeve 37, and the third main gas channel MG3 inside the insulation sleeve 37, to the fourth main gas channel MG4 between the insulation sleeve 37 and the replacement part unit 2 a. The main gas produces a swirling flow by passing from the fourth main gas channel MG4 through the communication channels 703, and is jetted into the fifth main gas channel MG5. The main gas that has produced the swirling flow passes through the sixth main gas channel MG6 and is jetted from the jetting hole 831 of the nozzle 8.

As illustrated in FIG. 1, an assist gas supply pipe 48 is connected to the base portion 33. The assist gas supply pipe 48 is connected to a second assist gas channel AG2 inside the nozzle seat 36 via a first assist gas channel AG1 inside the base portion 33. The first assist gas channel AG1 extends from the base end surface of the base portion 33 toward the external circumferential surface of the base portion 33. The second assist gas channel AG2 extends from the internal circumferential surface of the nozzle seat 36 toward the external circumferential surface of the nozzle seat 36.

The second assist gas channel AG2 is connected to a fourth assist gas channel AG4 between the holder 38 and the second retainer cap 5 via a third assist gas channel AG3 inside the holder 38. The third assist gas channel AG3 extends from the internal circumferential surface toward the external circumferential surface of the holder 38. The fourth assist gas channel AG4 is an annular channel between the external circumferential surface of the holder 38 and the internal circumferential surface of the second retainer cap 5.

The fourth assist gas channel AG4 is connected to a sixth assist gas channel AG6 between the first retainer cap 4 and the second retainer cap 5 via a fifth assist gas channel AG5 inside the second retainer cap 5. The fifth assist gas channel AG5 is a plurality of channels that extend from the internal circumferential surface toward the external circumferential surface of the second retainer cap 5. The sixth assist gas channel AG6 is an annular channel between the internal circumferential surface of the first retainer cap 4 and the external circumferential surface of the second retainer cap 5.

As illustrated in FIG. 29, the sixth assist gas channel AG6 is connected to a seventh assist gas channel AG7 between the nozzle 8 and the shield cap 10 via the plurality of communication channels 105 in the shield cap 10. The seventh assist gas channel AG7 communicates with the jetting hole 831 of the nozzle 8 and the jetting hole 104 of the shield cap 10.

The sixth assist gas channel AG6 is sealed from the abovementioned third cooling water channel W3 by an O-ring R4. The O-ring R4 is fitted into a recessed portion 44 provided at the tip end portion on the internal circumferential surface of the first retainer cap 4. The O-ring R4 comes into contact with the first external circumferential surface 13 of the shield cap 10. That is, the first external circumferential surface 13 of the shield cap 10 includes a seal surface 131 that comes into contact with the O-ring R4.

The insulation ring 9 is coupled to the nozzle 8 by press-fitting as mentioned above. The insulation ring 9 is also coupled to the shield cap 10 by press-fitting. Consequently, the seventh assist gas channel AG7 is sealed from the abovementioned third cooling water channel W3 by the insulation ring 9.

The assist gas flows from the assist gas supply source, through the first assist gas channel AG1 inside the base portion 33, the second assist gas channel AG2 inside the nozzle seat 36, the third assist gas channel AG3 inside the holder 38, the fourth assist gas channel AG4 between the holder 38 and the second retainer cap 5, and the fifth assist gas channel AG5 inside the second retainer cap 5, to the sixth assist gas channel AG6 between the first retainer cap 4 and the second retainer cap 5. The assist gas passes from the sixth assist gas channel AG6 through the communication channels 105 to produce a swirling flow, and is jetted into the seventh assist gas channel AG7. The assist gas that produces the swirling flow passes through the seventh assist gas channel AG7 and is jetted from the jetting hole 104 of the shield cap 10 along with the main gas.

1.5 Replacement Method of Replacement Part Unit

A replacement method of the replacement part unit 2 a will be discussed next. The replacement part unit 2 a is a consumable. As a result, the replacement part unit 2 a is attached to the torch body 3 in a detachable manner and is replaced with a new unit when wear advances to the extent that replacement is necessary. As illustrated in FIG. 29, the step portion 17 of the shield cap 10 is pressed in the axial direction by the edge portion of the opening 51 of the second retainer cap 5 in the plasma torch 1 a. Furthermore, the flange portion 14 of the shield cap 10 is clamped between the edge portion of the opening 41 of the first retainer cap 4 and the edge portion of the opening 51 of the second retainer cap 5. As a result, the replacement part unit 2 a is fixed. Consequently, the second retainer cap 5 is removed first when replacing the replacement part unit 2 a.

While the second retainer cap 5 is removed, the replacement part unit 2 a is held by the elastic force of the O-rings R2, R3, and R4. Therefore, the insulation guide 7 and the electrode 6 of the replacement part unit 2 a are drawn away from the insulation sleeve 37 by drawing the replacement part unit 2 a from the opening 41 of the first retainer cap 4 toward the tip end side. At this time, the contact piece 22 of the center pipe 20 slides along the internal circumferential surface of the electrode 6 and the electrode 6 is pulled out from the center pipe 20. As discussed above, the replacement part unit 2 a can be removed easily in an integrated manner from the torch body 3.

The first retainer cap 4 may be loosened before drawing the replacement part unit 2 a from the opening 41 of the first retainer cap 4 toward the tip end side. As a result, the flange portion 14 of the shield cap 10 is caught on the edge portion of the opening 41 of the first retainer cap 4 and pushed out. Consequently, the replacement part unit 2 a can be removed easily.

When attaching a new replacement part unit 2 a, the replacement part unit 2 a is inserted from the opening 41 of the first retainer cap 4 toward the base end side. As a result, the electrode 6 and the insulation guide 7 of the replacement part unit 2 a are inserted into the insulation sleeve 37. At this time, the center pipe 20 is inserted into the electrode 6 and the contact piece 22 of the center pipe 20 slides along the internal circumferential surface of the electrode 6.

When the second retainer cap 5 is attached onto the first retainer cap 4, the edge portion of the opening 51 of the second retainer cap 5 presses the step portion 17 of the shield cap 10 toward the base end side. As a result, the replacement part unit 2 a is pushed in toward the base end side until the base end surface 601 of the electrode 6 comes into contact with the tip end surface 342 of the electrode seat 34. Furthermore, the flange portion 14 of the shield cap 10 is clamped and held by the edge portion of the opening 41 of the first retainer cap 4 and the edge portion of the opening 51 of the second retainer cap 5, whereby the replacement part unit 2 a is secured.

In the plasma torch 1 a according to the present embodiment discussed above, the electrode 6 is energized due to the contact piece 22 of the center pipe 20 coming into contact with the internal circumferential surface of the electrode 6. Therefore, a structure for connecting the base end side cylindrical portion of the electrode 6 and the internal circumferential surface of the electrode seat 34 as in the conventional plasma torch is made unnecessary. As a result, the structure of the electrode 6 or the electrode seat 34 can be simplified. Moreover, the electrode 6 can be attached or detached easily without a specialized tool because the threaded structure for connecting the electrode 6 and the electrode seat 34 is made unnecessary. Furthermore, replacement of the torch body 3 is unnecessary even when energization fault occurs.

The contact piece 22 has elasticity to produce a counterforce when pressed in the radial direction of the pipe body 21. As a result, the contact piece 22 is urged toward the internal circumferential surface of the electrode 6 due to the elasticity. As a result, contact between the contact piece 22 and the electrode 6 can be made in a stable manner. Consequently, energization between the contact piece 22 and the electrode 6 can be carried out in a stable manner.

The contact piece 22 is separate from the pipe body 21 and is attached to the external circumferential surface of the pipe body 21. As a result, only the contact piece 22 can be replaced when the contact piece 22 is damaged. Consequently, costs can be reduced.

The internal channel 65 of the electrode 6 includes the tapered portion 652 that increases in size in the radial direction toward the inlet of the internal channel 65. As a result, the contact piece 22 can be inserted easily into the internal channel 65.

The first energization surface 603 is disposed adjoining the tapered portion 652 at the tip end side of the tapered portion 652. As a result, the distance in which the contact piece 22 slides in the internal channel 65 can be reduced when the center pipe 20 is inserted into and removed from the electrode 6. As a result, friction between the contact piece 22 and the electrode 6 can be reduced. Moreover, cooling brought about by the flow of the cooling water can be performed during operation because the contact piece 22 is inserted into the cooling water channel inside the electrode 6. As a result, energization with a large electrical current is possible even if the contact piece 22 acting an electrical conductor has a small cross-sectional area.

2. Second Embodiment

A plasma torch 1 b as in a second embodiment will be discussed next. FIG. 32 is a cross-sectional view along the center axis of the plasma torch 1 b according to the second embodiment. FIG. 33 is a cross-sectional view of the replacement part unit 2 b according to the second embodiment. FIGS. 34 and 35 are perspective views of the replacement part unit 2 b. FIGS. 36 and 37 are perspective views of the nozzle 8 according to the second embodiment.

As illustrated in FIG. 33, the first external circumferential surface 85 of the nozzle 8 includes a recessed portion 851. The recessed portion 851 is provided on the second nozzle portion 82. The recessed portion 851 is recessed toward the inside in the radial direction of the nozzle 8 and extends in the circumferential direction of the nozzle 8. The recessed portion 851 is disposed at approximately the same position as the tip end of the electrode 6 in the axial direction of the nozzle 8. The outer diameter of the bottom portion of the recessed portion 851 is smaller than the inner diameter of the internal circumferential surface 812.

The recessed portion 851 includes a first wall surface 852 on the base end side and a second wall surface 853 on the tip end side. The first wall surface 852 is inclined with respect to the radial direction of the nozzle 8. The second wall surface 853 extends in the radial direction of the nozzle 8. As illustrated in FIG. 32, the first wall surface 852 extends parallel to the inclined internal circumferential surface of the first retainer cap 4. The recessed portion 851 is disposed inside the third cooling water channel W3.

In the present embodiment, a plurality of holes 43 that communicate with the third cooling water channel W3 are provided in the first retainer cap 4. The holes 43 of the first retainer cap 4 communicate with an annular cooling water channel W12 between the first retainer cap 4 and the second retainer cap 5. The recessed portion 851 is disposed at approximately the same position as the holes 43 of the first retainer cap 4 in the axial direction of the nozzle 8.

Other configurations of the replacement part unit 2 b and the plasma torch 1 b are the same as those of the replacement part unit 2 a and the plasma torch 1 a of the first embodiment.

According to the abovementioned second embodiment, the recessed portion 851 is provided in the nozzle 8 whereby a greater surface area of the nozzle 8 comes into contact with the cooling water. As a result, the cooling performance of the nozzle 8 can be improved. Moreover, because the recessed portion 851 is disposed at approximately the same position as the holes 43 of the first retainer cap 4, the cooling performance of the nozzle 8 can be further improved. Further, the cooling water channel W12 is also able to supply cooling water to the second retainer cap 5. As a result, the replacement part unit 2 b according to the present embodiment is suitable for plasma cutting using a high electrical current.

3. Other Embodiments

Although embodiments of the present invention have been described so far, the present invention is not limited to the above embodiments and various modifications may be made within the scope of the invention.

The structures of the replacement part units 2 a and 2 b may be modified. The structures of the torch body 3, the first retainer cap 4, and the second retainer cap 5 may also be changed. The structure of the pipe body 21 or the contact piece 22 may be changed.

The electrode 6, the insulation guide 7, and the nozzle 8 may be coupled together in a detachable manner.

The electrode 6 and the insulation guide 7 may be coupled by adhesion instead of press-fitting. The insulation guide 7 and the nozzle 8 may be coupled by adhesion instead of press-fitting. The nozzle 8 and the insulation ring 9 may be coupled by adhesion instead of press-fitting. The insulation ring 9 and the shield cap 10 may be coupled by adhesion instead of press-fitting.

The insulation ring 9 and the shield cap 10 may not be included in the replacement part units 2 a and 2 b. That is, the replacement part unit may be configured by the electrode 6, the insulation guide 7, and the nozzle 8. Further, the insulation ring 9 and the shield cap 10 may be attached to the replacement part unit in an easily detachable manner.

The inner diameter of the gas channel inside the insulation guide 7 may be large than the inner diameter of the nozzle 8. That is, the inner diameter of the fifth main gas channel MG5 inside the insulation guide 7 may be greater than the inner diameter of the sixth main gas channel MG6 inside the nozzle 8 as illustrated in FIG. 38.

INDUSTRIAL APPLICABILITY

According to the present invention, a center pipe for a plasma torch, a contact piece, an electrode, and a plasma torch can be provided for which the electrode can be attached and detached easily without a specialized tool, the structure of the electrode or the electrode seat is simplified, and moreover, the replacement of the torch body is unnecessary even when energization fault occurs. 

What is claimed is:
 1. A center pipe for a plasma torch for plasma cutting, the plasma torch including a base portion and an electrode, the center pipe being inserted into the electrode in order to supply cooling water into the electrode, the center pipe comprising: a pipe body having a tube-like shape including a base end surface and a tip end surface opposite the base end surface in an axial direction of the tube-like shape, the pipe body being configured to be electrically connected to an electrical power source outside of the plasma torch via the base portion, the pipe body including a cooling water channel therein, and the pipe body being made of an electrically conductive material; and a contact piece arranged radially outside an external circumferential surface of the pipe body at an intermediate position between the base end surface and the tip end surface, the contact piece energizing the electrode through contact with an internal circumferential surface of the electrode, and the contact piece being made of an electrically conductive material, wherein the base end surface is disposed outside the electrode when the center pipe is inserted into the electrode, and the pipe body is configured to be electrically connected to the electrode via the contact piece.
 2. The center pipe according to claim 1, wherein the cooling water channel of the pipe body includes a first channel extending from the base end surface toward the tip end surface, and the first channel is tapered such than an internal diameter of the first channel is wider near the base end surface and narrower toward the tip end surface.
 3. The center pipe according to claim 1, wherein the cooling water channel of the pipe body includes a first channel, a second channel, and a third channel, the first channel extending in the axial direction of the tube-like shape from the base end surface toward the tip end surface, the second channel extending in the axial direction from a tip end surface side of the first channel toward the tip end surface, the third channel extending in the axial direction from a tip end surface side of the second channel toward the tip end surface, the third channel reaching the tip end surface, an internal diameter of the third channel being larger than an internal diameter of the second channel, and the third channel being configured to receive a protruding portion provided on an internal surface of a tip end of the electrode.
 4. The center pipe according to claim 3, wherein, the external circumferential surface of the pipe body includes a first external circumferential surface, a second external circumferential surface, and a third external circumferential surface that are disposed axially adjacent one another along the axial direction with the second external circumferential surface being disposed between the first external circumferential surface and the third external circumferential surface, the first external circumferential surface has a larger external diameter than the second external circumferential surface, the second external circumferential surface has a larger external diameter than the third external circumferential surface, and the first external circumferential surface surrounds the first channel.
 5. The center pipe according to claim 4, wherein the pipe body includes a flange portion having a larger external diameter than the first external circumferential surface of the pipe body, the flange portion being disposed at a base end of the pipe body and including the base end surface, and the center pipe is configured such that the electrical connection of the pipe body to the electrical power source outside of the plasma torch is established by contact of the base end surface of the pipe body against the base portion of the plasma torch.
 6. The center pipe according to claim 1, wherein the center pipe is configured such that the electrical connection of the pipe body to the electrical power source outside of the plasma torch is established by contact of the base end surface of the pipe body against the base portion of the plasma torch.
 7. The center pipe according to claim 6, wherein the pipe body includes a flange portion having a larger external diameter than the external circumferential surface of the pipe body, the flange portion being disposed at a base end of the pipe body and including the base end surface.
 8. The center pipe according to claim 1, wherein the pipe body includes a flange portion having a larger external diameter than the external circumferential surface of the pipe body, the flange portion being disposed at a base end of the pipe body and including the base end surface, and the contact piece is attached to the external circumferential surface of the pipe body.
 9. An electrode for a plasma torch for plasma cutting that includes a center pipe having a cooling water channel therein, the electrode comprising: an electrode body portion including a tip end and a base end, the tip end and the base end being spaced from each other in an axial direction of the electrode, the electrode body portion having a shorter length in the axial direction than the center pipe; and an internal channel configured to receive the center pipe, the internal channel being formed inside the electrode body portion and extending in the axial direction from the base end toward the tip end, a base end surface of the base end of the electrode including an inlet of the internal channel.
 10. The electrode according to claim 9, further comprising a protruding portion provided on an internal surface of the electrode body portion at the tip end, the protruding portion protruding toward the base end of the electrode body portion.
 11. The electrode according to claim 10, wherein the protruding portion is configured and arranged to be at least partially disposed inside a cooling water channel of the center pipe when the electrode and the center pipe are installed in the plasma torch.
 12. The electrode according to claim 11, wherein the protruding portion fits inside the cooling water channel at a tip end of the center pipe.
 13. The electrode according to claim 10, wherein a heat resistant insert is embedded into a tip end surface at the tip end of the electrode.
 14. The electrode according to claim 13, wherein the heat resistant insert is disposed at least partially inside the protrusion.
 15. The electrode according to claim 9, wherein at least a portion of an internal circumferential surface of the internal channel forms a first energization surface configured to be in contact with a contact piece of the center pipe.
 16. A plasma torch including the center pipe according to claim 1, the plasma torch further comprising: the base portion; and the electrode, the electrode including an internal channel having the internal circumferential surface into which the center pipe is inserted, at least a portion of the internal circumferential surface of the internal channel forming a first energization surface, which is in contact with the contact piece. 